There's quite a list of possibilities for a loss of power. Could be spark or could be fuel delivery. Common ailments are fuel filter, fuel pressure regulator, dirty MAF, stopped up EGR. Did you get a check engine light (CEL)?

On the transmission, I have heard more than once that if you are unsure of the age of the fluid in a tranny and it's maintenance schedule, you're better off to leave it be. This is obviously debatable, and I'm sure you could pay someone to change it. But you might be opening pandora's box. Might be best to keep the fluid topped off and hope for the best. Up to you though.

By the way, how many miles on the VX, and how many when you got it?